Suddenly developed difficulty getting shifter into all gears but engagement was normal (pedal well off the floor) - 264k miles on clutch. Replaced clutch cylinders for good measure (free with Autozone lifetime warranty) but that wasn't the problem as suspected. Friend's 94 GSR had exact same symptoms at 130k miles some years ago --> broken clutch disc hub causing slight drag on pressure plate. Sure enough, my disc had same problem. 2" long piece of hub plate at perimeter of a spring broke off and was causing slight drag...Linings looked virtually new --> only 35% worn (would last 700k miles at that rate) ! Replaced with OE-style Exedy kit. Noted the disc is 0.6 lb lighter than OE and pressure plate is 1.0 lb lighter than OE.

Decided to splurge for Exedy racing flywheel (measured 8.7 lb) to replace OE (measured 15.4 lb) based on same friend's experience going from 17 lb (OE) to 12 lb on his GSR. Even with 7.7 lb (30%) reduction in rotating weight (flywheel + pressure plate)I notice just about 0 difference except that engine accelerates faster in neutral (no-load acceleration) and matched-rev downshifts are easier/quicker, more like my AP1 (but still not as quick). Car is 2,170 lb which certainly helps with smooth launching but, again, there is little/no difference with lighter flywheel...